Semiconductor lasers and optical amplifiers are preferred in transceivers because they are efficiently electrically pumped and the die size is small. Lasing is a radiative recombination process in semiconductors, in which an electron in the conduction recombines with a hole in the valance band and a photon is emitted. The reverse process is electron hole pair generation through optical absorption, which occurs in such devices as photodetectors and solar cells.
Semiconductor, e.g. Silicon, photonics is widely seen as an enabling technology to address the exponentially increasing demand for data communication bandwidth. Lasers, in particular single mode and tunable lasers, are critical components in data transmission systems. Two fundamental elements of a laser include a gain medium and a resonating cavity. Due to the indirect bandgap of silicon, several approaches for introducing gain medium into the photonic integration material system have been disclosed, including edge coupled bonding, direct bonding, heavily N-doped germanium, and quantum dot structures. Single mode laser cavities are typically constructed with Distributed Bragg Reflectors (DBRs), which require high lithography resolution and which are sensitive to fabrication variations.
Practical semiconductor-based, e.g. silicon, light sources have still not been discovered, despite the progress in germanium lasers, because both silicon and germanium are indirect-band semiconductors and inefficient at light generation. Accordingly, this situation has propelled the study of group III/V-based laser integration onto a semiconductor, e.g. silicon or silicon-on-insulator (SOI), platform.
An object of the present invention is to overcome the shortcomings of the prior art by providing an external cavity laser for integrated semiconductor photonics.